a. Field of Invention
The present invention relates to downhole apparatus and particularly, but not exclusively, to downhole apparatus for use in releasing a stuck drill bit.
b. Description of Related Art
It is not uncommon for a drill bit to become stuck inhole during downhole oil and gas drilling operations. In order to allow retrieval of a downhole drill string when a drill bit becomes stuck, it is known to provide a drill string with an emergency release joint immediately uphole of the drill bit. During normal operation, the release joint transmits torque from a motor or string (from surface) to the drill bit. However, in the event that the drill bit becomes stuck to the extent that axial and rotational movement of the drill bit is not possible, the drill bit may be separated from the remainder of the drill string by virtue of the release joint. The remainder of the drill string may then be moved axially uphole so that specialist retrieving equipment may be run to the drill bit in a fishing operation.
Although the prior art release joints are effective in providing a system for releasing the drill bit from a wellbore, the steps of retrieving the drill string and subsequently running a fishing string is time consuming and expensive.
It is an object of the present invention to provide apparatus allowing a stuck drill bit to be conveniently, rapidly and inexpensively released from a wellbore.